Common house dust is an important cause of asthma, rhinitis, atopic dermatitis, eczema and other allergic conditions in sensitive individuals. Household dust generally comprises a variety of particulate matter including pollen, dust mites, dust mite allergens, dirt, skin cells, animal dander, insect parts, pillow feathers, food particles and mould spores. The particular constituents of dust will depend on location within the house, whether pets are present and other obvious factors. One of the principal sources of allergies is dust mites, which inhabit rugs, carpets, and other fabric surfaces, particularly sofas, mattresses, pillows, upholstered chairs and the like. The mite Dermatophygoides pteronyssinus has been identified as a major source of house dust allergen. This mite and the related mites D. farinae, D. microceras and Euroglyphus maynei are the predominant house dust mites in temperate climates in North America, Europe, Australia and other areas.
Dust mites are not insects, but are eight-legged arachnids, relatives to ticks and spiders. They live in close association with humans (or other mammals), their main food source being the shed scales from skin. Adult mites are approximately 300 microns (3/10 mm) in size, having developed over approximately 25 days through egg, larval and nymph stages. Adults live for 2 to 31/2 months, during which time each female can produce about 20-40 eggs. Dust mites are photophobic, living deep in pillows, mattresses, carpets, upholstered furniture and other soft materials.
In addition to a food source, the other essential requirement for dust mite growth is adequate humidity. Dust mites are 75% water by weight. They do not drink water, but must absorb water vapor from the air in order to survive. Specialized glands above their pairs of legs produce secretions high in sodium and potassium chloride, which act to absorb water vapor from surrounding air. This can only be accomplished if the surrounding humidity is sufficiently high. Relative humidities of about 65-80% at temperatures ranging from about 20 to 35 C are optimal for dust mite growth. Dust mites will die at humidities of 50% or less. In geographical areas where humidity is high, dust mites are present in nearly all homes and may be as plentiful as 18,000 mites per gram of dust. Literally millions of mites can inhibit a single bed or rug.
A major dust mite allergen is present in mite faecal particles. Each mite produces about 20 faecal particles per day, and more than 100,000 of them may be present in a gram of dust. These particles vary from about 10 to 40 microns in size, comparable to the size of pollen grains, and become airborne during domestic activity such as making beds and vacuuming carpets.
Group I allergens (dermatophagoides farinae I-Der f I and dermatophagoides pteronyssinus I-Der p I) are heat labile, 24,000 molecular weight glycoproteins (hydrolytic enzymes). These allergens appear to be structural homologues and have very similar N-terminal amino acid sequences. These group I allergens are regarded as the most important and are excreted in their highest concentrations by the mite's gastrointestinal tract in the form of mite's faecal particles, suggesting that they are associated with digestion. They elute rapidly (within 2 minutes) from isolated faecal particles, but very slow from mite bodies.
Group II allergens (Der p II and Der f II) are 15,000 molecular weight proteins with almost identical N-terminal amino acid sequences that are also secreted by the mite's gastrointestinal tract in the form of faecal allergens, although not in as high a concentration as the group I allergens. This suggests that they probably derived from a source other than the gut. Their actual function has not been determined.
Most mite-allergic individuals produce antibodies to both the group I and group II allergens.
______________________________________ Allergen Mol. Weight pH ______________________________________ Group I Der p I 24,000 4.6-7.4 Der f I 24,000 4.6-7.4 Group II Der p II 15,000 5.0-6.4 Der f II 15,000 7.8-8.3 ______________________________________
Acute exposure to mite allergens has been shown to induce wheezing, rhinitis, eustachian tube obstruction or eczema in sensitized patients. Chronic exposure can cause bronchial hyper-reactivity and chronic asthma. There is a correlation between the level of exposure to house dust mite allergen in early childhood and the likelihood of the subsequent development of asthma. Conversely, asthmatics sensitive to dust mites improve in environments without mites, such as at high altitudes or in hospital rooms. Attempts have therefore been made to decrease patients' exposure to dust mites in the home.
Studies of dust avoidance measures in homes have shown that the use of impermeable mattress and pillow encasings and the removal of bedroom carpeting are associated with a decrease in mite counts. These measures have also been shown to be of clinical value, with a decrease in symptoms and medication requirements occurring in children and adults with dust-sensitive asthma when pillows and mattresses are encased and carpets are removed.
Although carpets and upholstered furniture are major sites of dust mite growth, many allergic individuals are unable or unwilling to remove these from their home. Ordinary vacuuming does not remove dust mites or significantly decrease dust mite allergen levels, and in fact, vacuuming of carpets with the usual household appliances actually increases the amount of airborne dust. However, the use of special filters such as HEPA (High Efficiency Particulate Air) filters or two-ply vacuum bags, and/or the employment of central vacuuming systems (where the dust is collected in a receptacle remote from the room being cleaned) have been helpful. Nevertheless, vacuuming seldom removes all of the live mites, mainly because the mites have little suction cups on the tops of their legs which cause them to cling to textile fibres.
Various chemical agents have been used against mites, including: compounds known under the common names as resuethrin, phenothrin, permethrin, allethrins, tetramethrin, furamethrin, cypermethrin, decamethrin, phenvalerate, phenpropathrin, terallethrin, empenthrin and pyrethrin; pyrethroid compounds such as 1-ethynyl-2-methyl-2-pentenyl-2,2-dimethyl-3,3-(2,2-dichlorovinyl)-cyclopr opane-1-carboxylate, 1-ethynyl-2-methyl-2-pentenyl-2,2,3,3-tetramethylcyclopropane-1-carboxylat e, .alpha.-cyano-3-phenoxybenzyl-2,2-dimethyl-3-(2,2,3-tribromomethyl)-cyclop ropane-1-carboxylate; organic phosphorus compounds such as sumithion, fenthion, tetrachlorvinphos, diazinon and DDVP; and carbamate compounds such as those sold under the trademarks Baygon and Sevin. However, these conventional miticides are expensive and are often either toxic to human beings or have the potential themselves to cause allergic or other adverse reactions. Therefore, the use of such compounds in a household environment cannot be the solution to controlling the population of dust mites.
A number of less toxic miticidal agents have been proposed for use in controlling dust mites. As noted in U.S. Pat. No. 4,800,196, these include phenyl salicylate, diphenylamine, methyl beta-naphthyl ketone, coumarin, phenethyl benzoate, benzyl salicylate, phenyl benzoate, N-fluorodichloromethylthio-cyclohexene-dicarboxyimide, p-nitrobenzoic acid methyl ester, p-chlorometaxylenol, .alpha.-bromocinnamic aldehyde, 2,5-dichloro-4-bromophenol, 2-phenylphenol, sodium 2-phenylphenolate, 5-chloro-2-methyl-4-isothiazoline-3-one, 2-methyl-4-isothiazoline-3-one and benzimidazolylmethylcarbamate. These can be used in the form of solutions, wettable powders, granules, sprays, etc.
While many of these compounds have some degree of effectiveness against dust mites, their use is not without attendant shortcomings. For example, many of them are rather expensive to produce and/or may be difficult to form into compositions for ordinary domestic use. Elimination of dust in a household environment is a task which is intensely disliked to the point where the average householder is no longer embarrassed by a moderate layer of dust or the presence of "dust bunnies" under beds or behind furniture. Furthermore, as noted above, dust removal and/or vacuuming often stirs up the dust mites and their attendant allergens and, temporarily at least, causes more distress to allergic persons.
More effective methods of reducing exposure to dust mites and their faecal matter, have been developed which do not depend on the diligence of the householder in removing dust.
U.S. Pat. No. 5,271,947 features the use of finely divided sodium chloride powder as a method for killing mites and controlling their allergen-bearing faeces. The powder has the consistency of talcum powder and is used, for example, by applying the powder with a broom or brush to carpets and other textile materials. However, one of the disadvantages in using sodium chloride powder is its hygroscopicity; if the amount used is not carefully controlled, the salt will absorb moisture from the air, particularly in humid climates.
One of the more effective agents for killing dust mites is benzyl benzoate, a compound which is readily available and inexpensive. Powder formulations containing benzyl benzoate are commercially available for application to carpets. British Patent No. 1,368,657 teaches the use of a composition for treating bedding and similar materials which comprises benzyl benzoate and polyethylene glycol, or an ether or ester thereof, as an evaporation retarding agent. British Patent No. 2,042,893 teaches the use of a composition comprising benzyl benzoate and a fatty acid ester for application to bedding and also for treating the skin. A similar composition for general miticidal use in households is taught in published Japanese Patent Application No. 61-91103.
More generally, Bischoff U.S. Pat. No. 4,666,940 teaches the use of various miticidal agents, including particularly benzyl benzoate, as a component in cleansing compositions. The disclosed compositions can also contain dissolved or dispersed plastic materials, but said materials must form discrete particles of particular size and must not form a film.
European Patent Application No. 0,612,469 discloses laundry detergents comprising benzyl benzoate, which compositions are taught to be effective in killing the dust mites present on the articles to be laundered.
In an article by G. Schober et al., "Control of House-Dust Mites (Pyroglyphidae) with Home Disinfectants", Experimental & Applied Acarology 3:179-89 (1987), the authors provide data showing that the addition of benzyl benzoate to certain commercially available carpet cleaning formulations results in a composition with better acaricidal properties than other known acaricides.
U.S. Pat. No. 5,180,586 discloses that certain compounds, previously known for use as perfuming agents in foods and cosmetics, have been found to be effective in killing dust mites.
To summarize the published literature, it is apparent that benzyl benzoate and other miticidal compounds disclosed in the art can, under proper conditions of use, be effective in killing dust mites and thus helpful in reducing the level of allergens produced by said mites. Laundering and dry cleaning of textiles and fabrics can also be effective under certain conditions, but this is not practical for day-to-day control.
The principal problem associated with previous methods for controlling dust mites and their allergens is the fact that frequently the mites and their faecal particles are not completely removed. At best, compositions containing acaricidally effective compounds will kill off the mites, but will not remove their faecal matter and the associated allergens. Vacuuming, either by itself or as a final step in a method involving chemical treatment, is often not effective because the pick-up nozzle of the vacuum cleaner cannot effectively fit into all of the crevices in upholstered furniture. Furthermore, unless vacuuming is done under special conditions such as use of a two-ply vacuum bag or HEPA filter, the allergens will be dispersed into the ambient air, therefore doing more harm than good. Therefore, it would be desirable to have a method for controlling dust mites and their associated allergens which would avoid the various disadvantages of the methods heretofore used.
Accordingly, it is a principal object of this invention to provide improved methods for controlling dust particles, in particular, dust mites and the allergens present in their faecal excretions.
It is a further object of this invention to prevent the allergens present in dust and, in particular, dust mites, from entering into the ambient air of indoor spaces.
Another object of this invention is to provide compositions which can be used in attaining the aforementioned objects.